Photographic fixing agent



Patented Sept. 26, i93

zen-14,494 rno'roomrmc FIXING AGENT Robert Bowling Barnes, Stamford,

or to American Gyanamid Company,

Gonm; assign; New York,

N. Y., a corporation of Maine No Drawing. Application March 343, 1939,

Serial No. 264,975

8 Claims.

This invention relates to a photographic fixing composition and moreparticularly, to a photographic fixing and hardening bath.

The standard fixing baths for silver halide sensitized material dependon the solvent action of sodium thiosulfate on silver halide. Commercialsolutions usually contain in addition sodium sulfite, suificient acid tobring about the desired pH and, in the case of hardening baths, alum,chrome alum, and the like;

The fixers which are used at the present time have two disadvantages; Inthe first place, the fixing speed is only moderate and, in the secondplace; the baths become exhausted very rapidly. In fact, exhaustiontakes place when the amount of silver dissolved is only a few-percent ofthat corresponding to the sodiumthiosulfate present. A serious wastagein chemicals is thus encountered when spent fixing solutions have to bediscarded.

According to the present invention, the fixing solution contains anamidine ion and preferably .a guanidine ion in effective amounts. Theion may be introduced into the solution by using the correspondingamidine thiosulfate in place of part or all of the sodium thiosulfate ora salt of the amidine may be added to a fixer bath containing sodium oralkali metal thiosulfate. I do not know in just what form the amidineion is present but substantially the same results are obtainedregardless of whether'the amidine sulfate is first prepared or whetheran amidine salt is added to a sodium thiosulfate bath.

The presence of the amidine ion results in a material increase in fixingspeed. While this is a characteristic of all of the amidines, theydifferamong themselves in their effectiveness, guanidine showing thegreatest increase in speed. The presence of the amidine ion andparticularly the guanidine ion also increases the number of films orpaper prints which can be fixed in a given amount .of solution. In thecase of guanidine, this increase is most marked. I do not know exactlywhy the great increase in fixing capacity takes place when the guanidineion is present in the fixing bath. It is possible that the presence ofthe guanidine ion permits solution of larger amounts of silver halidebefore exhaustion and it is also possible that at least part of theeffect is due to the precipitation of silver in the metallic form by thepresence of the guanidine. Thus, for example, a fixer. containingguanidine thiosulfate after it has become loaded with dissolved silverprecipitates out a considerable portion of this" silver on standing.

The present invention is therefore not limited to any particular theoryas to why fixing solutions containing the guanidine ion show greatlyenhanced fixing capacity.

The present invention contemplates the use of fixing solutionscontaining any of the simple amidines. The increase in speed of fixingis greatest with guanidine and least with guanyl urea salts, whilebiguanides are intermediate in their efiect. The guanidine ion has thefurther advantage that fixing even of highly sensitized material such aspanchromatic and orthochromatic film does not produce any noticeablefog.

Some of the other amidines produce a small amount of fog. For thisreason, while the present invention broadly includes-the amidine ion, ina more specific aspect guanidine is the preferred amidine ion.

It is an advantage of the present invention that the amidine, andparticularly guanidine, ion does not appear to interfere with the othercomponents of the fixing solution. Thus, for example, guanidinethiosulfate may replace sodium thiosulfate in the standard fixingformulae, hardening or non-hardening, and similarly guanidine or otheramidine salts may be added to the standard fixing formulae. In the caseof guanidine, some care should be taken that the concentration ofguanidine thiosulfate, or rather the guanidine ion, does not reach toohigh a figure. Thus, for

example, if the concentration greatly exceeds that corresponding to 240parts by weight of guanidine thiosulfate per liter of fixing solution,reticulation may be noticed with certain negative material such as, forexample, fast panchromatic film.

Another important advantage of the use of guanidine thiosulfate is itsgreat solubility which permits perparing 50% solutions at 70 C. Highlyconcentrated liquid fixing baths can therefore be prepared which canthen be diluted for use.

Guanidine thiosulfate in the dry form is stable and can be readilyincorporated with other components to form a mixed, dry fixing powderwhich can be dissolved in water to form a fixing solution. Mixtures ofguanidine salts and sodium thiosulfate can also be readily made and havesatisfactory keeping qualities.

The invention will be described in greater detail in conjunction withthe following specific examples which illustrate typical fixing bathsaccording to the present invention.

Example 1 A fixing bath was prepared as follows:

. Parts Water at 52 C 600 Guanidine thiosulfate 240 Sodium sulfite,desiccated" Acetic acid, 28% 48 Boric acid, crystal 7.5 Potassium alum15 Water at C 400 The solution has a pH of 4.45 and is very stableagainst sulfurization. The solution clears u'nex-' posed Eastmanorthoportrait film in 1% minutes at 24 C. as compared with 3 minutes fora standard Eastman F5 fixing solution in which sodium thiosulfate takesthe place of guanidine thiosulfate. The gelatin hardness of the stripswas evaluated by melting point tests and showed that the fixer. usingguanidine thiosulfate produced slightly harder gelatin having a meltingpoint up to 95 or 96 C. as compared to 93 C. for a standard sodiumthiosulfate fixer such as Eastman F5. The fixed films were ofsatisfactory color, flexibility and showed unreticulated surfaces freefrom fog. Increased amounts of guanidine thiosulfate causes the bath tofix more rapidly but when the amount is considerably increased there isa tendency to reticulate the film.

When a number of films or other silver halide photographic material havebeen fixed and the solution is allowed to stand in a glass bottle,metallic silver begins to plate out on the walls of the containerwhereas with an ordinary sodium thiosulfate fixing solution such asEastman F5 practically no precipitation takes place until the solutionis almost exhausted. Actinic light appears to have some acceleratingaction on the precipitation of silver from the guanidine thiosulfatefixing bath.

The keeping qualities of the guanidine thiosulfate solution areexcellent. A particular solution was prepared and showed 1 minutesclearing time with a pH of 4.45. After 5 months, the clearing time wasabout the same with a pH of 4.4 and after 10 months, the clearing timewas still about 1 minutes with a pH of 4.05. Before the last test, thesilver which had precipitated was removed byfiltration, leaving a clearfiltrate.

A test was made to determine the limit of exhaustion of the guanidinesolution as compared with Eastman F5, in which solution the amount ofsodium thiosulfate is the same as that of guanidine thiosulfate in theguanidine thiosul- 3 minutes at 24 fate fixer. A small portion (100 cc.)of each solution was taken and unexposed Eastman orthoportrait filmswere cleared in both solutions. In the fresh solution the clearing timefor the guanidine fixer was 1 minutes and in Eastman F5, C. Clearingtimes after the solutions had been used were measured and the results ofthe tests appear in the following table:

Clearing time in minutes Negative material'flxed, square inches 32Eastman F5 Did not completely clear.

Further use of the guanidine thiosulfate solution did not affect theclearing time even after 625 sq. ins. had been cleared. The longer lifeof the guanidine thiosulfate fixer is of great practical importance asone of the largest .costsin large scale photographic processing "is .theconsumption of fixer as the bath has to be discarded long before itschemicals are exhausteddue to the fact that with sodium thiosulfateafter a small amount of-silver has been dissolved the solution no longershows rapid clearing power.

Ihave not determined definitely the reasons for the extraordinarybehaviour of guanidine thiosulfate solutions and do not wish to limitthe present invention to any theory of action. I

believe, however, that at least one factor lies in the precipitatingaction which the guanidine thiosulfate has on the dissolved silver. Thisappears also more likely from a consideration of the exhaustion curve.It will be noted that the guanidine thiosulfate solution slows upgradually until around 500 sq. ins. is reached and then it remains at afixed level which makes it seem probable that an equilibrium is beingreached between the precipitating action for metallic silver and theadditional silver halide dissolved. The fixing action is, however, toocomplex to permit ready determination of whether this factor is the onlyone or even whether it is the predominant one and this explanation isadvanced merely as a possible one without limitation on the invention.

Example 2 An Eastman F5 fixing solution was prepared and varying amountsof guanidine nitrate were added to successive 200 cc. portions and theclearing times of the resulting solutions with Eastman orthoportraitfilm were measured. The

An exhaustion test on orthoportrait film was then run with the followingresults:

Negative material fixed, square inches gg Minutes From the above itsappears that the addition of guanidine nitrate produces a fixing bathhaving essentially similar properties to that in which uanidinethiosulfate itself was added. It is probable that some of the guanidinenitrate reacts with sodium thiosulfate to form guanidine thiosulfate butI do not believe that the presence of guanidine thiosulfate as such isessential, the presence of the guanidine radical or iron beingsufiicient. It is interesting to note that even the largest amount ofguanidine nitrate added was less than that theoretically required toreact with all of the sodium thiosulfate.

Example 3 I A standard F5 fixing solution wasprepared and to separate200 cc. portions guanidine nitrate, hydrochloride and carbonate wereadded in the noted that in the case of potassium chrome alum fixers, thefixer frequently does not have as good amounts described in Example 2(12 gs.) and Example 3. The solutions were then tested in clearingEastman Panchro Press cut film. The fixing times were as follows:

Fixing time in Firing solution I minutes Eastman F5 4. 25

Eastman F5+guanidine nitrate 2.

Eastman Ffiiguanidine hydrochloride 2. 75

Eastman F5 guanidine carbonate 3. 75

Times for clearing will vary with diflerent films but as is shownabove-remain in substantially similar proportions.

Example 5 The Eastman F5 solution was prepared and 5 gs. of biguanideacid sulfate was added to 200 cc. The clearing time for Eastmanorthoportrait film was 2.25 minutes. A slight permanent chemical fog wasnoticed on the film but not sufficient to materially interfere withprinting quality.

Example 6 5 gs. of guanyl urea sulfate was added to 200 cc. of EastmanF5. It did not dissolve entirely and the saturated solution produced wasused in clearing orthoportrait film. The time was 3.25 minutes and aslight permanent chemical fog was produced somewhat heavier than withthe biguanide sulfate.

In the examples the fixing solutions are of the ordinary potassium alumtype. The presence of the amidine radicals has the same speed increasingand life increasing properties with fixing solutions which do notcontain hardening agents or with those in which potassium chrome alum isused in place of potassium alum. It should be keeping qualities as isthe case with potassium alum fixers. The presence of the guanidineradical or iron in every case produces a. bath of high stability but ifthe composition of the bath is such as to render it of poor keepingqualities, the presence of a guanidine radical or amidine radical willnot turn a bath having poor keeping qualities into one havinggood-keeping qualities.

What I claim is:

1. A silver halide photographic fixing agent of the thiosulfate typecontaining an amidine salt in amounts efiective to increase the fixingspeed.

2. A silver halide photographic fixing agent of the thiosulfate typecontainin a guanidine salt in amounts effective to increase the fixingspeed.

3. A silver containing guanidine thiosulfate as its major silver halidedissolving agent.

- 4. An acid silver halide photographic fixing and hardening agent ofthe thiosulfate type containing an amidine salt in amounts effective toincrease the fixing speed and a hardening agent.

5. An acid silver and hardening agent of the thiosulfate type containinga guanidine salt in amounts effective to increase the fixing speed and ahardening agent. 6. An acid silver halide photographic fixing andhardening agent of the thiosulfate type containing a guanidine salt inamounts eflective to increase the fixing speed and an alum.

I. A silver halide photographic fixing agent of the thiosulfate typecontaining a biguanide salt halide photographic fixing agent halidephotographic fixing in amounts effective to increase the fixing speed. 1

8. A silver halide photographic fixing agent of the thiosulfate typecontaining a guanyl urea salt in amounts efiective to increase thefixing speed.

ROBERT BOWLING BARNES.

